Miller et al. Journal of Animal Science and Biotechnology (2016) 7:61 DOI 10.1186/s40104-016-0121-9
RESEARCH
Open Access
Dietary stimulation of the endogenous somatotropic axis in weaner and growerfinisher pigs using medium chain triglycerides and cysteamine hydrochloride David W. Miller1*, Zoe Prosser1, Edward Y. W. Chee1, Christian F. Hansen2, Frank R. Dunshea3, Bruce P. Mullan4 and John R. Pluske1
Abstract Background: Three experiments were conducted to examine the overall hypothesis that addition of medium chain triglycerides (MCT) and cysteamine hydrochloride (CSH) into the diets of young and growing pigs would stimulate the endogenous somatotropic axis to improve growth and performance. Results: In Experiment 1, weaner pigs were given either a 5 d dietary supplement of 5 % MCT (n = 8) or a control diet (n = 8). MCT increased the plasma concentration of growth hormone (GH; P < 0.05) and the GH secretagogue, ghrelin (P < 0.05). Additionally, the MCT treatment reduced scouring (P < 0.05), maintained villous height in the small intestine (P < 0.05) and stabilised daily weight gain (P < 0.05), compared to the controls. Experiment 2 compared the effects of 4 levels (0, 1, 3 and 6 % v/v) of MCT supplementation in grower-finisher male pigs, of approximately 35 kg live weight (n = 15 per treatment). Blood samples taken after 7 wk of treatment showed that the MCT supplementation increased circulating ghrelin (P < 0.001), GH (P < 0.01) and insulin (P < 0.05) concentrations in a dose-dependent manner. Daily weight gain, feed intake and feed conversion ratio were not affected by the MCT diets. In Experiment 3, 64 female pigs of approximately 60 kg live weight were allocated to one of three dietary treatments: control (n = 20); 6 % MCT (n = 21); and 70 mg/kg CSH (n = 21). After 3 wk of supplementation, the MCT treated pigs had a higher plasma concentration of ghrelin compared to the control and CSH pigs (P < 0.05). Plasma concentrations of GH and weight were not affected by any of the dietary treatments. Conclusions: Evidence is provided in Experiment 1 to support the use of dietary MCT supplements, perhaps acting via stimulation of somatotropic endocrine pathways, to minimise weaning-associated disorders such as slowing of growth and diarrhoea. In Experiments 2 and 3, although there was no effect on weight gain or feed conversion ratio in either experiment, MCT and CSH increased endocrine components of the somatotropic axis. Keywords: Ghrelin, Growth, Pig, Somatotropin
* Correspondence:
[email protected] 1 School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Miller et al. Journal of Animal Science and Biotechnology (2016) 7:61
Background Porcine somatotropin (growth hormone; GH), is approved for use in pigs in many countries worldwide [1], although not in the USA or European Union, to improve daily weight gain and promote lean growth. Growth hormone is a protein whose secretion from the somatotrophs of the anterior pituitary gland is regulated by two hypothalamic neurohormones that specifically act to either stimulate (via GH-releasing hormone, GHRH) or inhibit (via somatostatin) the release of GH [2]. The overall effects of GH are to enhance the ability of muscle cells to utilise nutrients, while simultaneously coordinating other physiological processes and tissues (such as adipose tissue), in a manner that supports enhanced lean growth [2]. Previous studies have investigated dietary means of increasing endogenous GH levels. Dietary inclusion of the sulfhydryl compound, cysteamine hydrochloride (CSH), increases GH secretion in rats [3], sheep [4, 5] and fish [6]. The increase in GH secretion is due to the inhibitory effect of CSH on somatostatin release [5]. Dietary supplementations of CSH at 30 mg/kg and 50 mg/kg of feed resulted in significant increases in daily weight gain in finisher pigs, but had no effect on plasma concentrations of GH [7]. A dietary supplementation of CSH at 70 mg/kg of feed in finisher gilts caused an increase in daily weight gain, but GH levels were not measured in this study [8]. Ghrelin, a GH-releasing peptide initially isolated from the stomach of rats [9], stimulates GH release from the anterior pituitary gland [10]. Studies have identified multiple physiological functions for ghrelin in mammals, including GH release, appetite stimulation, cellular proliferation, apoptosis inhibition, and regulation of lipid metabolism and tissue fat distribution in muscle [11–15]. Ghrelin is also reported to be involved in the inhibition of proinflammatory cytokine production and gastroprotection against stress-induced gastric damage in rats [16, 17]. Moreover, Salfen et al. [18] showed that ghrelin infusion for 5 d increased GH secretion and concomitantly increased weight gain in weaner pigs. The major active form of ghrelin is a 28-amino acid peptide containing an octanoic (C8:0) fatty acid on the third amino acid (serine) of the peptide [19]. The post-translational C8 modification is essential for biological activity of ghrelin to allow binding to its receptor, which causes the release of GH at the level of the pituitary [19]. It has been reported that ingested medium chain triglyceride (MCT) oil derived from coconuts, which contain high levels of octanoic acid, are directly utilised for the bio-activation of ghrelin in rats [19]. However, no studies to date in pigs have looked at the effect of dietary MCT on somatotropic growth responses and the involvement of bioactive ghrelin levels in the circulation. Three experiments were conducted to examine the overall hypothesis that addition of MCT and CSH into
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the diets of young and growing pigs would stimulate the endogenous somatotropic axis to improve growth and performance. The aims of Experiment 1 were to investigate whether the addition of MCT to the diet of weaner pigs would increase the biological activation of ghrelin in the circulation, and if increasing the amount of biologically-active ghrelin would promote GH release. The aim of Experiment 2 was to determine the optimal inclusion rate of MCT into the diets of grower-finisher pigs to investigate somatotropic growth responses, and in Experiment 3, a comparison of the effects of MCT with a CSH dietary supplement for grower-finisher pigs was conducted.
Methods These experiments were approved by the Animal Ethics Committees at both Murdoch University (NS1176/06, NS2173/08, NS2253/09) and the Department of Agriculture and Food WA (5-05-33, 2-08-9, 2-09-18) to ensure compliance with the guidelines of the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes. All experiments were conducted at the Medina Research Station, Department of Agriculture and Food WA, Medina, WA, Australia. Experiment 1
Twenty four, 21-day-old Large White x Landrace pigs (12 females and 12 intact males), with an average body mass of 5.12 ± 0.24 kg (S.E.M.), were initially allocated into 2 indoor pens (12 pigs per pen) measuring 1.5 m × 1.5 m, and the indoor pens were kept at a constant temperature of 28 °C. The pigs remained in these group pens for 5 d to acclimatize to the post-weaning artificial milk diet. Each pen contained a nipple drinker for water and two milk drinkers. During the 5 d of acclimatization, the pigs were provided with a commercial artificial milk diet prepared from Pigiplus® (Biostarch P/L, Wendouree. Vic., Australia), as per instructions, with the addition of 50 g of dried bovine colostrum (Nufarm Colostrums, Laverton, Vic., Australia) and 50 mL of a probiotic (Pro B, Dandenong, Vic., Australia) per 8 L of Pigiplus ®. Pigiplus ® contains approximately 14 % fat (as solids when reconstituted), 22 % protein, 43 % lactose and 0.2 % fibre. At 2-h intervals the milk feeders were cleaned and fresh milk added. After the acclimatization period, 16 pigs (8 males and 8 females) were chosen for the experiment based on their health status (e.g., normal feed intake, normal weight gain, no or minimal scouring). These pigs were separated into single indoor pens of 1.5 m × 0.75 m containing a nipple water drinker and a milk drinker. The pigs were then randomly allocated to the 2 treatments, ensuring that there were equal numbers of each sex, similar sibling relationships and similar group weights between the
Miller et al. Journal of Animal Science and Biotechnology (2016) 7:61
treatments. The two treatments were a Control group fed a milk replacer diet (n = 8; Pigiplus®) and a MCT group fed the same milk replacer with the addition of 5 % (v/v of prepared milk replacer) MCT (MCT Oil; Melrose Laboratories Pty Ltd, Mitcham, Vic., Australia) (n = 8) in an homogenous solution. The MCT oil supplement was a refined form of coconut oil containing octanoic acid (C8) (65–75 %), decanoic acid (C10) (25–35 %), and hexanoic acid (C6) (
